No single favorite for me, depends on the salad and my mood.
We often make a lemon-olive oil-garlic dressing for just a simple green salad. I like a spicy chipotle ranch when I'm having a southwest type salad with beans, corn, crumbled tortilla chips. If I'm having it with grilled salmon on top, or with roasted veggies, I like honey mustard. I like a ginger dressing if I'm having a salad along with an Asian inspired meal. Poppyseed dressing is my choice when I've got fruit in the salad. If I'm at an Italian restaurant I'll usually go with balsamic vinaigrette. I love Thousand Island, but only occasionally on a green salad ... I add it to my grilled cheese & tomato on rye sandwiches, and once in awhile add it to a burger. Italian dressing goes in one of the pasta salads that I make, and occasionally as a marinade, but rarely on my green salad. Those are probably the ones I use most frequently. I've also got green goddess in my fridge right now that is pretty good, but I got it as a dip for cut veggies on a specific occasion, and probably won't have it regularly.
No blue cheese dressing for me though, never.